Fluctuations In Primary Production Research Articles

Seasonal Primary Productivity Variation in Shatiya Wetland of Gopalganj (Bihar)

The primary productivity is basic aspect to understand water quality and fishery potentials. The water samples were analyzed for physico-chemical parameters and light and dark bottle method used to quantify productivity. The results indicated that productivity greater than respiration showed positive relationship with required biomass at wetland sites to productivity. The primary producers constitute a significant position in trophic limit in wetlands and showed fluctuations in net and gross primary production along with community respiration and chlorophyll content. These parameters exhibited bimodal fluctuations in primary productivity during summer and winter seasons except monsoon period. Seasonal variation in the rate of primary production does not remain same throughout the year.

Using remotely sensed indicators of primary productivity to improve prioritization of conservation areas for top predators

The need to incorporate habitat dynamics into spatial conservation prioritization is increasingly recognized but often limited by the lack of available temporal data. To overcome this limitation, model-assisted monitoring has been advocated and developed over the last decade. However, predictive modelling often relies on static habitat features or interpolated climate data, failing to consider other relevant ecological processes such as primary productivity and its dynamics. The importance of primary productivity relies on its key role in determining the availability of food resources via trophic cascades. This study aims to assess how the spatiotemporal variation in the habitat quality for top predators (using raptors as case study) can be affected by temporal fluctuations in primary productivity, and whether its incorporation into habitat modelling improves predictions in space and time. Through model predictions we then incorporate interannual habitat-quality dynamics into spatial conservation planning to identify priority areas for raptor conservation based on a new set of dynamic priority-area indices. Using raptor occurrence data from two surveys (2001 and 2014), we found high model performance and transferability for all species (AUC2001 = 0.89 ± 0.10 and Boyce’s Index2001 of 0.78 ± 0.20; AUC2014 = 0.89 ± 0.12 and Boyce’s Index2014 of 0.87 ± 0.06). Annual mean and minimum values of EVI (indicators of productivity and phenology, respectively) and elevation were the most important predictor variables for most raptor species. However, the standard deviation of EVI (an indicator of seasonality) was also found to be an important predictor for migratory species breeding in shrublands and croplands. Interannual model predictions showed a large interannual variation in habitat availability across species, partially associated with regional land-use changes. Interannual habitat-quality dynamics was translated into marked changes in the priority areas for raptor conservation —areas mostly associated with deciduous forest and water environments (rivers and dams) in our study area. Our results shed light on the role of intra- and interannual dynamics of primary productivity in driving habitat quality for top predators. They also confirm the potential of remotely sensed ecosystem functioning attributes to inform about habitat-quality dynamics in a cost-effective, standardized and repeatable way. Incorporating interannual dynamics of primary productivity in habitat modelling supports raptor conservation prioritization by informing about adequacy, stability and legacy of raptor conservation areas.

Global diversity patterns are modulated by temporal fluctuations in primary productivity

AbstractAimTo evaluate the role of seasonal and non‐seasonal productivity fluctuations in global patterns of species richness.LocationWorldwide.Time period2000–2017.Major taxa studiedAmphibians, birds, mammals.MethodsWe analysed time series of monthly variation of the Normalized Difference Vegetation Index (NDVI), a surrogate of primary productivity, within c. 100 km × 100 km cells across all continents, estimating the mean, periodic seasonal variation and aperiodic unpredictable fluctuations of the NDVI in these cells. We then explored the relationships between mean NDVI and the components of its temporal variation and evaluated the independent effects of the above‐mentioned variables on species richness in the three vertebrate groups by means of variation partitioning.ResultsThere is a hump‐shaped relationship between mean productivity and variation in productivity, so that temporal variation in productivity is lowest in regions with minimum and maximum values of mean productivity. Although mean productivity is a strong determinant of species richness, both seasonal and non‐seasonal productivity variation significantly affect the species richness of all studied taxa when accounting for mean productivity. However, the direction of these effects differs between regions differing in the mean productivity level. High variation in productivity has a negative effect on species richness in regions with moderate to high productivity levels, whereas species richness is higher in arid regions with high variation in productivity.Main conclusionsSpecies richness is affected by temporal variation in productivity, but these effects differ regionally. In productive areas, high environmental stochasticity may increase population extinction rates, whereas arid regions probably benefit from resource fluctuations that promote species coexistence. Our results indicate that contemporary changes in patterns of temporal resource fluctuations may affect future global patterns of biological diversity on Earth.

Strength of a Trophic Cascade Between an Apex Predator, Mammalian Herbivore and Grasses in a Desert Ecosystem Does Not Vary with Temporal Fluctuations in Primary Productivity

There has long been debate regarding the primacy of bottom-up and top-down effects as factors shaping ecosystems. The exploitation ecosystems hypothesis (EEH) predicts that predators indirectly benefit plants because their top-down effects limit herbivores’ consumption of plants, and that the strength of trophic cascade increases with increasing primary productivity. However, in arid environments, pulses of primary productivity produced by irregular rainfall events could decouple herbivore–plant and predator–prey dynamics if high conversion efficiency from seed biomass to consumers allows the rapid build-up of consumer populations. Here, we test predictions of the EEH in an arid environment. We measured activity/abundances of dingoes, red kangaroos and grasses, and diet of dingoes, in landscapes where dingoes were culled or not culled over 3 years. Dingo activity was correlated with rainfall, and their tracks were less frequent at culled sites. Kangaroo abundance was greater at sites where dingoes were culled and increased with rainfall in the previous 6 months. Grass cover was greater at sites where dingoes were not culled and increased with rainfall in the previous 3 months. During a period of average rainfall, dingoes primarily consumed rodents and increased their consumption of kangaroos during a period of drier conditions. Our results are consistent with the hypothesis that suppression of an apex predator triggers a trophic cascade, but are at odds with the EEH’s prediction that the magnitude of trophic cascades should increase with primary productivity. Our study demonstrates that temporal fluctuations in primary productivity can have effects on biomasses of plants and consumers which are in many ways analogous to those observed along spatial gradients of primary productivity.

Variability in primary productivity determines metapopulation dynamics.

Temporal variability in primary productivity can change habitat quality for consumer species by affecting the energy levels available as food resources. However, it remains unclear how habitat-quality fluctuations may determine the dynamics of spatially structured populations, where the effects of habitat size, quality and isolation have been customarily assessed assuming static habitats. We present the first empirical evaluation on the effects of stochastic fluctuations in primary productivity—a major outcome of ecosystem functions—on the metapopulation dynamics of a primary consumer. A unique 13-year dataset from an herbivore rodent was used to test the hypothesis that inter-annual variations in primary productivity determine spatiotemporal habitat occupancy patterns and colonization and extinction processes. Inter-annual variability in productivity and in the growing season phenology significantly influenced habitat colonization patterns and occupancy dynamics. These effects lead to changes in connectivity to other potentially occupied habitat patches, which then feed back into occupancy dynamics. According to the results, the dynamics of primary productivity accounted for more than 50% of the variation in occupancy probability, depending on patch size and landscape configuration. Evidence connecting primary productivity dynamics and spatiotemporal population processes has broad implications for metapopulation persistence in fluctuating and changing environments.

Zn isotope evidence for immediate resumption of primary productivity after snowball Earth

The Ediacaran period began with the deglaciation of the ca. 635 Ma Marinoan snowball Earth and the deposition of cap dolostones on continental shelves worldwide during post-glacial sea-level rise. These carbonates sharply overlie glacial sediments deposited at low paleolatitudes and preserve negative carbon isotope excursions. The snowball Earth hypothesis invokes an almost complete cessation of primary productivity in the surface ocean. Because assimilatory uptake of Zn appears to fractionate its isotopes, Zn isotope ratios measured in carbonate precipitated in the surface ocean should track fluctuations in primary productivity. Here we report the first Zn isotopic data, together with carbon and oxygen isotopic profiles from a Neoproterozoic cap dolostone, the Nuccaleena Formation in the Flinders Ranges, South Australia. We interpret the Zn isotopic data in terms of a two-stage evolution of the deglacial ocean. Slightly ^(66)Zn-enriched values at the base of the cap dolostone indicate immediate resumption of the biological pump upon melting of the surface ocean, but this signal was diluted by intense surface runoff that drove δ^(66)Zn (^(66)Zn/^(64)Zn, versus the JMC Lyon reference) values down to the composition of continentally derived Zn. A subsequent rise in δ^(66)Zn records a vigorous increase in primary production and export from a nutrient-laden surface ocean.

Links between iron input and opal deposition in the Pleistocene equatorial Pacific Ocean

Iron is often a limiting nutrient in ocean regions that have a constant supply of other macro-nutrients, and changes in iron supply over time have been linked to fluctuations in primary productivity. Marine sediments from the equatorial Pacific Ocean show that over the past million years, iron input was linked to the export and burial of biogenic silica.

Consumers can enhance ecosystem productivity and stability in changing environments

AbstractThere is increasing interest in the impacts of pulsed resource inputs (e.g., seasonal fluctuations in primary production) on ecosystem properties. However, theoretical models have focused on the ecosystem role of consumers only in stable environments. We investigated how the consumption rate affects ecosystem properties when resource supplies are pulsed using a simple model with numerical simulations. We initially investigated how primary production responds to resource supply shortages under various consumption rates and found that a vigorous consumer attenuates a rapid reduction in primary production. We next examined ecosystem properties under pulsed resource supplies. Intermediate consumption enhances primary production. The consumption rate that maximizes productivity differs for producers and consumers in a given resource supply environment, irrespective of the pattern of pulsation. The enhancement of primary production and the maximization of secondary production occur simultaneously in a stable environment but are not always the same when the resource supply is pulsed. We also investigated the variability of primary production and found that intermediate consumption rates reduce its coefficient of variation. In addition, we found that consumers with either very low or very high consumption rates are vulnerable to extinction when resource supplies are pulsed. Therefore, consumers with intermediate consumption rates contribute not only to the enhancement and stabilization of primary production but also to the stability of the consumer population itself.

Frozen Evolution: Or, That's not the Way It Is, Mr. Darwin: A Farewell to Selfish Gene. By Jaroslav Flegr; translated by, Madeleine Štulíková. Prague (Czech Republic): Charles University in Prague Press. $20.99 (paper). 225 p.; ill.; index of texts in grey boxes and general index. ISBN: 978‐80‐86561‐73‐8. [Originally published as Zamrzlá evoluce aneb, Je to jinak, pane Darwin, by Academia,

Previous articleNext article No AccessNew Biological BooksFrozen Evolution: Or, That's not the Way It Is, Mr. Darwin: A Farewell to Selfish Gene. By Jaroslav Flegr; translated by, Madeleine Štulíková. Prague (Czech Republic): Charles University in Prague Press. $20.99 (paper). 225 p.; ill.; index of texts in grey boxes and general index. ISBN: 978‐80‐86561‐73‐8. [Originally published as Zamrzlá evoluce aneb, Je to jinak, pane Darwin, by Academia, Prague, Czech Republic, 2006.] 2008.Dan GraurDan GraurBiology & Biochemistry, University of Houston, Houston, Texas Search for more articles by this author Biology & Biochemistry, University of Houston, Houston, TexasPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 85, Number 4December 2010 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/656859 Views: 29Total views on this site Citations: 15Citations are reported from Crossref Copyright © 2010 by The University of Chicago Press. All rights reserved.PDF download Crossref reports the following articles citing this article:John Augusteyn, Maree Rich, Georgeanna Story, Barry Nolan Canids potentially threaten bilbies at Astrebla Downs National Park, Australian Mammalogy 43, no.33 (Jan 2021): 300.https://doi.org/10.1071/AM20034Manu E. Saunders, Deborah S. Bower, Sarah Mika, John T. Hunter Condition thresholds in Australia’s threatened ecological community listings hinder conservation of dynamic ecosystems, Pacific Conservation Biology 27, no.33 (Jan 2021): 221.https://doi.org/10.1071/PC20040Ian J. Radford, Leigh-Ann Woolley, Ben Corey, Tom Vigilante, , Ed Hatherley, Richard Fairman, Karin Carnes, Antony N. Start Prescribed burning benefits threatened mammals in northern Australia, Biodiversity and Conservation 29, no.9-109-10 (Jun 2020): 2985–3007.https://doi.org/10.1007/s10531-020-02010-9Benjamin Feit, Anna Feit, Mike Letnic Apex Predators Decouple Population Dynamics Between Mesopredators and Their Prey, Ecosystems 22, no.77 (Mar 2019): 1606–1617.https://doi.org/10.1007/s10021-019-00360-2Jennifer D. Noble, Scott L. Collins, Alesia J. Hallmark, Karin Maldonado, Blair O. Wolf, Seth D. Newsome Foraging strategies of individual silky pocket mice over a boom–bust cycle in a stochastic dryland ecosystem, Oecologia 190, no.33 (Jun 2019): 569–578.https://doi.org/10.1007/s00442-019-04432-xAnnabel L. Smith Successional changes in trophic interactions support a mechanistic model of post-fire population dynamics, Oecologia 186, no.11 (Nov 2017): 129–139.https://doi.org/10.1007/s00442-017-4016-zMike Letnic, Anna Feit, David M. Forsyth Strength of a Trophic Cascade Between an Apex Predator, Mammalian Herbivore and Grasses in a Desert Ecosystem Does Not Vary with Temporal Fluctuations in Primary Productivity, Ecosystems 21, no.11 (Apr 2017): 153–165.https://doi.org/10.1007/s10021-017-0141-0Zunchi Liu, Tong Liu, Hang Yu, Zhiquan Han, Tao Wang, Huafeng Liu Efficient sampling of plant diversity in arid deserts using non-parametric estimators, Biodiversity and Conservation 26, no.55 (Jan 2017): 1225–1242.https://doi.org/10.1007/s10531-017-1296-xHelen P. Waudby, Sophie Petit Small Australian desert vertebrate responses to grazing intensity during La Niña, Ecological Research 30, no.44 (May 2015): 715–722.https://doi.org/10.1007/s11284-015-1274-2Stephanie J. S. Yip, Maree-Asta Rich, Chris R. Dickman Diet of the feral cat, Felis catus, in central Australian grassland habitats during population cycles of its principal prey, Mammal Research 60, no.11 (Dec 2014): 39–50.https://doi.org/10.1007/s13364-014-0208-7Aaron C. Greenville, Glenda M. Wardle, Bobby Tamayo, Chris R. Dickman Bottom-up and top-down processes interact to modify intraguild interactions in resource-pulse environments, Oecologia 175, no.44 (Jun 2014): 1349–1358.https://doi.org/10.1007/s00442-014-2977-8Thomas M. Newsome, Guy-Anthony Ballard, Peter J. S. Fleming, Remy van de Ven, Georgeanna L. Story, Christopher R. Dickman Human-resource subsidies alter the dietary preferences of a mammalian top predator, Oecologia 175, no.11 (Feb 2014): 139–150.https://doi.org/10.1007/s00442-014-2889-7David L. Dunkerley Vegetation Mosaics of Arid Western New South Wales, Australia: Considerations of Their Origin and Persistence, (May 2013): 315–345.https://doi.org/10.1007/978-94-007-5727-1_12Chris R. Dickman Fences or Ferals? Benefits and Costs of Conservation Fencing in Australia, (Oct 2011): 43–63.https://doi.org/10.1007/978-1-4614-0902-1_4Louise A. Pastro, Christopher R. Dickman, Mike Letnic Burning for biodiversity or burning biodiversity? Prescribed burn vs. wildfire impacts on plants, lizards, and mammals, Ecological Applications 21, no.88 (Dec 2011): 3238–3253.https://doi.org/10.1890/10-2351.1

Fecal chlorophyll describes the link between primary production and consumption in a terrestrial herbivore

Spatiotemporal variation in primary productivity is known to have strong and far-reaching effects on herbivore ecology, but this relationship is often studied indirectly at broad scales, in part due to the difficulty in measuring selection for green biomass by individual animals. In aquatic systems, the concentration of chlorophyll in herbivore feces has been used as a direct measure of the consumption of photosynthetic primary production, but this method has not been applied to terrestrial systems. We measured chlorophyll concentration in feces from elk (Cervus elaphus) experiencing large fluctuations in primary production in the winter to spring transition over three years. We compared temporal trends in fecal chlorophyll with trends in fecal nitrogen, grass chlorophyll, grass digestible nitrogen, and landscape-level primary productivity (as described by the normalized difference vegetation index or NDVI). We also directly examined the relationship between fecal chlorophyll and NDVI. Temporal trends in fecal chlorophyll were strong and well described by piecewise regression (adjusted coefficient of determination, r(2)a = 0.881-0.888), showing uniformly low concentrations throughout winter followed by an abrupt, rapid increase beginning on different Julian days (88, 91, or 110) each year. Changes in fecal chlorophyll closely matched the temporal trend in the chlorophyll and digestible nitrogen concentration of forage grasses collected directly from elk feeding sites. Fecal chlorophyll also tracked broad temporal patterns in fecal nitrogen and NDVI, but discrepancies between the indexes may highlight preferences or constraints on selectivity for green biomass in elk. Spatially and temporally matched NDVI and fecal chlorophyll estimates were uncorrelated until NDVI reached approximately half its seasonal range. Combined, these data describe important patterns in selection for nutritious, green biomass in a temperate herbivore that would be difficult to study without data on fecal chlorophyll. Fecal chlorophyll produced novel and precise descriptions of (and detected large interannual differences in) winter length, severity, and the rate of spring green-up, as they were experienced by a large, grazing herbivore. Measuring fecal chlorophyll provides a noninvasive, inexpensive, and direct approach to describe an important aspect of foraging ecology in terrestrial herbivores and may be particularly powerful for studying climate effects in seasonal environments.

Disentangling marine, soil and plant organic carbon contributions to continental margin sediments: A multi-proxy approach in a 20,000 year sediment record from the Congo deep-sea fan

A 20 kyr long sediment sequence from the Congo deep sea fan (core GeoB 6518-1), one of the world’s largest deep sea river fans, has been analysed for bulk and molecular proxies in order to reconstruct the marine, soil and plant organic carbon (OC) contributions to these sediments since the last glacial maximum. The bulk proxies applied, C/N ratio and δ 13C org, ranged from 10 to 12.5 and from −24.5 to −21‰ VPDB, respectively. As molecular proxies, concentrations of marine derived alkenones and terrestrial derived odd-numbered n-alkanes were used, which varied between 0.2 and 4 μg/g dry weight sediment. In addition, the branched vs. isoprenoid tetraether (BIT) index, a proxy for soil organic matter input, was used, which varied from 0.3 to 0.5 in this core. Application of binary mixing models, based on the different individual proxies, showed estimates for terrestrial OC input varying by up to 50% due to the heterogeneous nature of the OC. Application of a three end-member mixing model using the δ 13C org content, the C/N ratio and the BIT index, enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary OC pool. The results show that marine OC accounts for 20% to 40% of the total OC present in the deep sea fan sediments over the last 20 kyr and that soil OC accounts for about half (∼45% on average) of the OC present. This suggests that soil OC represents the majority of the terrestrial OC delivered to the fan sediments. Accumulation rates of the plant and soil OC fractions over the last 20 kyr varied by a factor of up to 5, and are strongly related to sediment accumulation rates. They showed an increase starting at ca. 17 kyr BP, a decline during the Younger Dryas, peak values during the early Holocene and lower values in the late Holocene. This pattern matches with reconstructions of past central African humidity and Congo River discharge from the same core and revealed that central African precipitation patterns exert a dominant control on terrestrial OC deposition in the Congo deep sea fan. Marine OC accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions. These variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind-driven upwelling.

Oligocene shallow marine foraminifera from the subsurface of southern Hokkaido

Foraminiferal faunas from the Upper Oligocene Minaminaganuma Formation recovered from boreholes of the Yufutsu Oil and Gas Field and MITI Umaoi located in southern Hokkaido are characterized exclusively by the large elphidiids Elphidium mabutii and Cribroelphidium ombetsuense. They indicate cold water temperatures and an inner to middle sublittoral paleobathymetry. The total organic carbon (TOC) content and hydrogen index (HI) values obtained by CHN Corder and Rock-Eval pyrolysis indicate the significant deposition of organic carbon of phytoplankton origin in the inner sublittoral condition. Elphidium mabutii and C. ombetsuense show ubiquitous distribution suggesting high tolerance of these two species against environmental stresses such as fluctuations in primary productivity (nutritional condition). This newly recognized shallow marine fauna is located between the Eocene-Oligocene Poronai-Momijiyama fauna (agglutinated foraminifera dominant) and the Miocene Takinoue fauna (Ammonia dominant). A comparison between the thickness of strata and the range of paleobathymetric changes in the study area suggests that an equilibrium between basin subsidence and sediment accumulation existed to keep this area under shallow marine conditions during a certain period in the Late Oligocene, which preceded the rifting of the Japan Sea during the Early Miocene.

Fluctuation of biogenic and abiogenic sedimentation on the Shatsky Rise in the western North Pacific during the late Quaternary

Sedimentation of biogenic and abiogenic components was studied in cores NGC108 (36°36.85′N, 158°20.90′E; water depth 3390 m) and S2612 (32°19.84′N, 157°51.00′E; water depth of 2612 m) from the Shatsky Rise to understand fluctuations in primary productivity and abiogenic sedimentation in the mid-latitude of the western North Pacific during the late Quaternary. The mean C Organic/N atomic ratio of 6.0–7.8 in both cores indicates that organic matter is mainly marine in origin. Organic carbon is positively correlated with biogenic opal in core NGC108 in contrast to a weak correlation in core S2612. Although the maxima of paleoproductivity estimates in both cores generally occur during glacial times, the paleoproductivity estimates, biogenic opal/carbonate ratios and the C Organic/C Carbonate ratios have always been higher in core NGC108 than in core S2612 during the last 180 kyr, suggesting that the surface water at site NGC108 could have been influenced more by Subarctic water mass than at site S2612. However, the opal/carbonate ratio in core S2612 remains fairly constant relative to that in core NGC108, which might mean that the transition zone between Subarctic and Central water was narrower in latitude in at the oxygen isotope stage (OIS) 2/3 boundary, OIS 4 and OIS 6. Sedimentation of 13 inorganic elements has been measured in both cores. These elements are classified into four groups based on correlation between each element in content: (1) terrigenous components (Al, Ti, Fe), (2) biogenic calcareous material (Ca, Sr), (3) biogenic-scavenged elements (Mg, Zn, Cr, Be), and (4) the other elements (Mn, Ba, Cu, Ni). The terrigenous mass accumulation rates were elevated in OIS 2, 3 and 4 and late OIS 6 in core NGC108 while they were higher in early OIS 1, OIS 2, 4 and 6 in core S2612. MnO 2 and Ba might be redistributed during the sub-surface reduced condition. Especially precipitation of particle-reactive Be, which could be accelerated by both enhanced terrigenous input and biogenic vertical transport, has fluctuated largely in response to climatic change because of its short residence time (on the order of the oceanic mixing time).

Application of Artificial Neural Networks (ANN) to Primary Production Time-series Data

An artificial neural network (ANN) model was applied for predicting primary productivity (PP) from a 12 year time series (1985-1996) of monthly observations on a set of environmental and climatic variables from the Gullmar Ford (south-western Sweden). Results indicate a good fit between observed and predicted PP values. ANN can be regarded as a novel tool for primary production modelling and more generally when the numbers of environmental and climatic co-variates are large. ANN models fitted the data with a lower root mean square error of prediction (RMSEP) than more conventional and classic methods, such as multiple regression. Predictions of future changes in primary production from the same set of input variables using network set-ups with PP leading the input variables by 1, 2 and 3 month lags indicated that RMSEP was about the same as for the case with no lag. These results show the possibility of generating patterns of future fluctuations in primary productivity using ANN.

Monitoring forest degradation in tropical regions by remote sensing: some methodological issues

SummaryKey issues related to the monitoring by remote sensing of open forest degradation in a tropical context are discussed. Degradation of forest‐cover is often a complex process, with some degree of ecological reversibility and a strong interaction with climatic fluctuations. Only a representation of land cover as a continuous field of several biophysical variables can lead to an accurate detection of forest degradation. For this purpose, repetitive measurements of spectral, spatial and temporal indicators of the land surface have to be performed. Each set of indicators brings a specific type of information on the land cover. These indicators must therefore be combined to achieve a comprehensive description of the surface processes. The detection of inter‐annual changes in landscape spatial structure is more likely to reveal long term and long lasting land‐cover changes, while spectral indicators are more sensitive to fluctuations in primary productivity associated with climatic fluctuations. Different monitoring systems may be optimal for different ecosystems. A long time series of observations is always required. The monitoring of the spatio‐temporal distribution of biomass burning may also give indications of open forest degradation.

Foraminiferal dissolution at shallow depths of the Walvis Ridge and Rio Grande Rise during the latest Cretaceous: Inferences for deep-water circulation in the South Atlantic

Abstract A high-resolution (10–20 kyr) record of variations in CaCO3 content and dissolution was established for latest Cretaceous (last 0.7 Myr) deep-sea sediments from the South Atlantic Ocean (DSDP Site 516 from the Rio Grande Rise, and sites 525 and 527 from the Walvis Ridge). The degree of fragmentation of planktonic foraminifera (DFP) was used as a measure of calcite dissolution. High negative correlations between DFP and other independent measures of carbonate dissolution (percentage of sand fraction, absolute abundance of planktonic foraminifera, and planktonic/benthic foraminiferal ratio) validate its use as a sensitive index of calcite dissolution in upper Maastrichtian deep-sea sediments. Very high DFP and a significant negative correlation between DFP and CaCO3 content suggest that Site 516 was located below the foraminiferal lysocline during the entire interval studied. Such a shallow position of the lysocline (paleodepth of Site 516 was 1.2 km) may be explained by “upwelling” of corrosive deep waters along the southern margin of the Rio Grande Rise. Sites 525 and 527 were located above the foraminiferal lysocline; however, three short periods of enhanced dissolution were recognised at Site 525 (paleodepth 1 km) and one interval of strong dissolution was identified at Site 527 (paleodepth 2.7 km). The lack of correspondence between the dissolution regimes at sites from the Walvis Ridge suggests limited deep-water communication across this physiographic barrier. Two of the dissolution maxima recognised at Site 525 correspond to carbonate maxima at Site 527. Variations in “upwelling” intensity along the Walvis Ridge, resulting in fluctuations in primary productivity in this area, may be the proximal cause of both carbonate cycles at Site 527 and dissolution cycles at Site 525. We suggest that development of the bottom Ekman layer between a hypothetical westward geostrophic current and the topographical height of the Rio Grande Rise-Walvis Ridge system may be a plausible hydrodynamical explanation for the proposed “upwelling” along the southern margin of this topographical structure.

Trend, seasonality, cycle, and irregular fluctuations in primary productivity at Lake Tahoe, California-Nevada, USA

Primary productivity has been measured routinely at Lake Tahoe since 1967, and a number of mechanisms underlying variability in the productivity record have now been identified. A long-term trend due to nutrient loading dominates the series. Seasonality also is prominent, apparently controlled by direct physical factors unrelated to the trophic cascade. A 3-yr cycle has been detected and several possible mechanisms are considered. Irregular fluctuations also are present, caused in part by isolated events (a forest fire) and recurring but variable phenomena (spring mixing). Except possibly for the 3-yr cycle, the known sources of variability appear to operate ‘bottom-up’ through direct physical and chemical effects on the phytoplankton.

Reconciling particulate organic carbon flux and sediment community oxygen consumption in the deep North Pacific

THE mineralization of organic carbon in the deep ocean has been considered an enigma in the North Pacific. Comparisons of the supply of particulate organic carbon (POC) with estimates of its mineralization to CO2 by the sediment community have indicated that the supply of POC sinking into the benthic boundary layer may be as much as 97% short of meeting the organic carbon demand of the sediment community1,2. These previous findings were based on short-time-series measurements (<14 days) conducted in situ with sediment traps and benthic respirometers. We report here a comparison of long-time-series measurements (2.3 years) of POC flux into the benthic boundary layer and concurrent, seasonal measurements of sediment community oxygen consump-tion. We chose a single abyssal station (4,100 m depth) in a region of the eastern North Pacific where there is a strong seasonal fluctuation in primary production, and where previous studies1,2 showed the supply of POC to be as much as an order of magnitude lower than the demand by the sediment community. Our measure-ments, using the same methods, show agreement to within 15% between organic carbon supply and demand. This reconciliation is attributable to the inclusion of previously undetected episodic inputs of POC into the benthic boundary layer. These episodic inputs are critical to sustaining the sediment community at this station, and are probably important in other deep-sea environments where seasonal fluctuations in primary production are prominent in surface waters.

Interannual fluctuations in primary production: Direct physical effects and the trohic cascade at Castle Lake, California

Direct physical effects and cascading trophic interactions operate together to determine interannual variability in the seasonal pattern of primary productivity at Castle Lake, California. Principal component analysis was used to investigate the depth‐time distributions of productivity for summers 1961–1986. Two characteristic patterns were found, together accounting for 60–70% of the year‐to‐year variability. The first pattern corresponds to the deep productivity maximum that forms in the hypolimnion in June and July. Variability in this first pattern arises from the direct effects on phytoplankton populations of year‐to‐year changes in timing of ice breakup and hydraulic flushing in spring. The first pattern is unusually strong or weak, compared to the long‐term average, during the phenomenon of El Niño‐Southern Oscillation. A second characteristic pattern corresponds to the mixed‐layer productivity maximum that develops in August and September. Variability in this second pattern arises from trophic interactions at higher levels: rainbow trout feed on late‐summer Daphnia rosea populations, which in turn graze on the mixed‐layer algal community. In addition, some of the variability in the rainbow trout population arises from year‐to‐year differences in angling pressure from humans. These results demonstrate how interannual variability in an ecosystem property (primary productivity) can be controlled by forces acting simultaneously through the top and the base of the food web.

Interannual fluctuations in primary production: Meteorological forcing at two subalpine lakes

Meteorological factors are associated with most of the interannual variability in primary production at both Castle Lake, California (41°N, 122°W) and Lake Tahoe, California‐Nevada (39°N, 120°W). At Castle Lake, extreme values of annual primary production, either much higher or lower than the long‐term average, are likely to occur during the phenomenon of El Niño/Southern Oscillation. Two plausible pathways for the impacts of these large‐scale climate events at Castle Lake were identified: winter snowfall, acting through its effect on the snow‐ice pack and timing of the spring thaw; and total precipitation, acting through its effect on outwash rates. In contrast, no influence of large‐scale climate events is apparent at Lake Tahoe, but a plausible pathway involving the impact of synoptic‐scale phenomena on interannual variation was identified: local weather events occurring in the late winter‐early spring period near the time of minimal stratification, acting through their effect on the depth of spring mixing. The difference between the two lakes can be attributed to absence of an ice cover and long hydraulic retention time at Lake Tahoe. Time‐series models that incorporate meteorological information adequately forecast primary production at both lakes.